There are a few four-letter words that are often heard in the Maintenance Industry. There are however also two other four-letter words that should be heard more often. They are

MTBF – Mean Time Between Failures

MTTR – Mean Time to Repair

These two words are not just acronyms for more reports, they represent powerful and simple-to-use tools for organisations to improve their maintenance functions and to become more profitable.

In today’s world where industry is anxious to increase profitability, what better way to increase than to decrease expenditure. Savings are not just directly related to maintenance costs but are more directly related to the huge costs of lost production through machine failures.

So what do these tools do and how do you use them?

If you want to plan for improved maintenance and extend the longevity of equipment and/or plan for the replacement of machines then the tool to use is MTBF. This measures how long a system or machine is expected to operate before it fails and will help organisations to understand the availability of equipment and also highlight any reliability issues that may exist.

If however, you are wanting to minimise downtime and reduce repair costs, then the right tool is MTTR. This measures how long it takes to repair a machine after it fails. It is a powerful metric and is used to measure how well equipment or services are being maintained, and how quickly issues are being responded to.

Let’s have a closer look at both of these powerful tools and how effective their use can be

MTBF measures the average time between system breakdowns. Understanding mean time between failures is a crucial maintenance metric to measure performance, safety, and equipment design, especially for critical or complex assets. It can be calculated as the arithmetic mean time between failures of a system.

Not only do maintenance practices change, but operating parameters change as well and processes are run faster or slower to produce more or less product according to market demands. As product specifications change, they, in turn, change the process’s average running conditions and changes in temperature, pressure, speed, flow, and viscosity can all affect machinery life in unknown or unquantifiable ways.

We need to be able to measure the impact of these changes on our maintenance organisation.

 MTBF Formulae

Total working time minus total downtime divided by the number of incidents


Total working time = 20 days

Breakdowns = 4 of 0.5 days each

Total breakdown time = 2 days

Calculation = 20 minus 2 divided by 4 = 4.5 days

Result = 4.5 which is the average running time for the machine between breakdowns

MTBF is the tool that measures the average running time and helps us to increase that time and reduce the number of incidents through maintenance initiatives.

MTTR does NOT represent Mean Time Between Failures. It represents Mean Time to Repair and this includes Repairs due to Failures, Planned Maintenance and/or any other type of Repair events.

MTTR measures the average time it takes to recover from a machine or system failure. This includes the full time of the outage—from when the machine or system fails to when it becomes fully operational again. It is measured from the moment that a failure occurs until the point where the equipment is repaired, tested and available for use.

MTTR is vitally important and is one of the most commonly used metrics available to maintenance operations, with the objective of minimising the impact of the expense and disruption of downtime

With the rapid pace of life and business these days, responding as quickly as possible to issues when they arise can sometimes mean the difference between retaining or losing business. Measuring MTTR ensures that you know how you are performing and can take steps to improve the situation as required.


Total Maintenance time over a period divided by the number of repairs


Number of repairs = 4

Individual maintenance times (hours) = 3 + 6 + 7 + 4 = 20 hours in total

Calculation = 20 divided by 4 = 5 hours

MTTR is the tool that measures the average maintenance repair time so we can evaluate how well equipment or services are being maintained, and monitor our improvement efforts.


These tools should be actively available with any reputable maintenance management product as they are critical tools for industry improvement.

So the next time you hear a few four-letter words in your maintenance environment, let’s try and make sure they are the words that will add value to your organisation and your improvement initiatives.

Have a happy maintenance day!!!!

Contact Joe  Schoeman and the Schorp  Group  Team for more information.

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